Electric braking system



May 18, 1926: 1,585,439

R. N. THOMAS L ELECTRIC BRAKING SYSTEM Filed May 31, 1924 Y VOW/06 2 Y [Z93 NT/romas.

His Attqrngy Fri-tented May 18, 1926.

warren, stares earner series;

RGY N. THOMAS, OE EAiSTOR'ANGE, ITEVI JERSEY, ASSZEGNOR TO COMPANY, A OURPGRATION OF NEW YOPIK.

GENERAL ELECTRIC Application: filed May 31,

My invention relates to improvements in hrakingsystems and more particularly to braking systems for electric motor driven machines such as printing presses and the, like wherein electrically operated friction hralgesare applied upon the opening of the driving motor circuit.

An object of the invention is to provide an improved braking system embodying automatic means for applying electrically operated brakes with varying degrees of intensity. v

A further object of the invention is to provide an electric braking system'for an alternating current electric motor driven machine in which a direct current operated friction brake is applied with increasing intensity upon the disconnection of the-driving motor.

In carrying my invention into effect in a preferred form, an alternating current electric motor driven machine such as for example a'printingpress, is provided with an electrically operated friction brake which is biased to the released position, together with a device for transformingalternating current to direct current, the device being arranged to be connected to a source of alternating current upon the energization of the; alternating current driving motor of themachine and to the brake upon the de-enengizat-ion of the driving motor, In order to prevent too severe an application of the brake when the press is rotating at high speed an automatic means is set into operation upon the de-energization of the driving motor to gradually increase the energization of the electrically operated brake after theapplication thereof.

For a better understanding of my invention, reference is had to the following description taken in connection with the accompanying drawing which diagrammatically illustrates a control systemfor an electric motor driven printing press embodying my improved braking system for the purpose of explaining the principles thereof.

Referring tothe drawing, it will beseen that a small starting motor l0 of the alternating currentsquirrel cage induction type and a large variable speed running motor 11 of the alternating current phase wound rotor induction type are provided for oper- 1924; Serial No. 716,885.

ating the printing press (not shown). It will he understood that the armature shafts l2 and 13 ofthe' respective motors are connectedthroughsuitable mechanical gearing (not shown) to drive the press, the gearing connecting the shaft 12- preferably being of the speed reducingtype in. order to permit the small motor lO'to startand jog the press at a low speed r .7 7

An electromagnetic line switch 14: is provided forconnecting the small motor 10 to the alternating current supplyline 15, 16' and 17 with the current limiting resistances 18 an electromagneticin circuit therewith and line switch 19 is arranged toopen and close the energizing circuit ofthe running motor 11. v i c Provision is made for operating the running motor 11 at a plurality of speeds by connecting the rotor windings thereof in circuit with. the speed regulating resistances and 17 for operation in either direction; re v sponsively to operation of onefof: the.nor mally open manual in the drawing as"Slo The Slow jog. and the also cooperate with auxiliary s nism controlled by the speed controller to effect the energization'of the'startingand driving motor line switches 14 and '19 as will more fully appear in 'connectionaw-ith' w-jog and Fast.

the description of theoperation of my ina vent-ion. r

For braking the press driven bythe motors l0 and 11, the-electrically operated frictionbrakesQr" and QSarearranged to ongage respectively with the cooperating braking drums '29 and 30. Although the brake drums 99 and 30 are shown as mounted upon the armature shaft 13 of the running mot-or 11, it willbe understood that. the braking;

drums may be mounted on a rotating part of the press if desired. As shown the frictron. brake 27 is ofthe type whlch'is biased push. buttons; indicated Fast push buttons witch inechato the-braking position and is operated there from upon connection of'the operating winding with which the brake is provided to the alternating crrront it will be observed however that and is operated to the braking position responsivelv encrgization of the operating windi In tier to ellect a smooth and steady application or" the brake 28 at all times as well as to permit applicationthereof with varying degrees of intensity, I provide a variable voltage source of direct current for energizing the winding 32. In the preferred form shown, the motor generator set coinposed of the alternating currentmotor 33 and the variable voltage direct current generator 3 1 having a shunt field winding 35 and a commutatingfield winding36 comprise a device for transforming alternating current from the supply lines 15,16 and 17 to direct current suitable for operating the brake 28. The connection oft-he driving motor 33 to the supply lines 15, 16 and '17 is controlled by the electromagnetic switch 37 and the electromagnetic switch 38 controls the connection of the generator 34L to operating winding 32 of the brake 28 and as will subsequently appear, the arrangement is such that the motor generator is placed in 1 standby service upon the operation of the press by the running motor 11 and is maintained in service until after the press is brought to a standstill under the combined braking effect of the brakes 27 and 28. A regulating resistance 89 connected in the shunt field circuit of generator 3 1 is controlled by the normally closed electromagnetic switch to'vary the voltage 01 genera: tor 34.

A normally closed time elementrelay 41 is provided with suitable retarding means such as the adjustable dashpot shown, or may be or" the well known wattmeter type. The purpose of this device as well as thatot the auxiliary switch mechanism with which the electromagnetic line'switches 14 and 19, the reversing switch and the speed controller 23 are respectively provided as well as the push buttons indicated as Safety and Stop in the drawing will be betterunderstood from the following description of the operation of my invention.

lVith thesupply lines 15, 16 and 17 connected to a suitable source of alternating current and with the disconnecting switch 42 in the closed position, the small motor 10 may be individually energized to start and operate the printing press at slow speed by manual operation of the Slow-jog push button from the open position in which it is shown to the closed position. This establishes an energizing circuit for the operating winding of the electromagneticline switch 14.- which may be traced as fol lows from other suitable biasin means ler 23 the supply line 16 through the middle pole oi the control disconnecting switch 1-2, the conductor 50,the Safety push button switch in the closed position, the Slow-jog push button switch, conductor '51, the auxiliary contact on the reversing switch 25, conductor 52, and the segment 53 the contacted, and the segment 55 of the speed controller 2S,*the conductor v6 and then through the operat ing winding of electromagnetic switch and the contact'of the overload relays 57 and 58 and the left hand blade of disconnecting switch 42 to the supply line The electromagnetic line switch 1 1- at once responds and connects the motor 10 with the current limiting resistances 18, in circuit to the supply lines 15, 16 and 17, for jogging operation of the press. The closing of line switch 14: also establishes an energizing circuit for the operating winding ofthe el ctromechanical brake 2"? since one terminal of the winding is connected directly to the supply line 17 and the other terminal is connected through the blade 59 of the line switch 1 1 to the supply line 15. Upon the release of brake 27 the press is gradually started and accelerated to a low jogging soeed. The jogging operation of the press however is continued only as long as the Slow-jog push button is maintained in the closed position.- Vl hen released the Slowyog push button returns to the open PO81- tion according to its bias and nterrupts the energizing circuit of the operating winding of line switch 141- thus disconnecting both the motor 10 and the operating winding of bralre 27 from the supply lines 15, 16 and 17 and the braking effect of the latter soon stops the press. i

It now it is desired to start and accelerate the press to one of the several running speeds, the normally open Fast push button is closed to energize the operating winding of the pilot motor reversing switch through a circuit extending roan the supply line 16 through the middle blade of the disconnecting switch 12, the conductor 50, the Safety switch in the closed position, the Fast push button, conductor 60, limit switch 61, the operating winding of switch 26, and through the left hand blade of disconnecting switch 12 to supply line 15. lhe resulting closure of reversing switch 26 connects the pilot motor 24: to the supply lines 5, 16 and 17 for operation in the direction required to rotate the speed control in counterclockwise direction. When the speed controller 23 hasv rotated suiiiciently to bring the sliding contact 54 into engagement with the segment 62,Jthe operating winding of the electromagnetic line switch 1 1- is energized through a circuit extending from the conductor 60 through the auxiliary contact mechanism 63, sell ment 62 sliding contact 54;, seginent55, con- Laziness,

ductor 56 and thence through the operating winding of electromagnetic line switch 1 1 to the supply line 15.

Line switch 1% at once closes and connects the starting motor 10 to the supply lines 15, 16 and 17 with the current limiting resistances 18 in circuit therewith and the motor 10 starts the press and accelerates the same to a low speed. 7

1t will be observed that a holding circuit for the operating winding of the elctromagnetic line switch 14 is established upon the closure thereof through the Stop button, the auxiliary contact 67 in its upper position, the conductor 68, the segment 62, contact 54, segment 55 of the controller 23, and then through the conductor 56 and the operating winding of switch 14. Thusthe Fast push button may be released and the motor 10 will continue operation of the press at a slow speed which is suitable for threading the press during the make-ready period.

To start the driving motor 11 and accelerate the press to one of the operating speeds, the Fast push button is again closed to reconnect the pilot motor 2 1 tothe supply lines 15, 16 and 17 through the reversing switch 26 and continue the rotation of the speed controller 23 in a counterclockwise direction lVhile the sliding conact 5% is still in engagement with the segment 62, the auxiliary contact mechanisms 63 and 6a are simultaneously closed. Closure of contact 6-1 completes an energizing circuit for the operating winding of the electromagnetic line switch 19 extending through the Fast push button, the conductor 60, the auxiliary contact mechanism 64:, the conductor 65, the auxiliary contact 66 of line switch 14 and then through the operating winding of line switch 19, to the supply line 15. Thus the line switch 19 is energized to close and connect theinotor 11 to the supply lines. 15, 16 and 17 with all of the resistances 20, '21 and 22 connected in the rotor circuit of motor 11. Motor 11 at once startsand accelerates the press to its lowest running speed. Itwill be seen that a holding circuit for the operating winding of line switch 19 is established through the stop button and the. auxiliary contact 69 in its upper position when the switch 19 is closed. Also an energizing circuit for the winding of the electro-mechanical brake 27 is completed through the upper blade of the line switch 19. Closure of contact 63 completes an energizing circuit for the reversing .switch 26 in shunt to the Fast button which may be ti'aced as follows, from the conductor 50 through Stop button, auxiliary contact 67 in the upper position, conductor 68, contact 63, and the limit switch 61 to the winding'ofelectromagnetic switch 26. Hence even though the st button. is released, the pilot motor speedcontroller 23 .si'iificiently to disengage the contact 5 1 from the segment 62 and at.

the same time open the auxiliary contact mechanisms 63 64, the energizing circuit of electromagnetic SWltClT 14 is interrupted and the small motor 10 is disconnected from the supply lines 15, 16 and 17. The press then is driven entirely by the large motor 11, at the slowest speed thereof which substantially corresponds to the jogging speed of motor 10. It will be seen that if the Fast button has been returned to the open position the energizing circuit of reversing switch 26 also is interrupted by the opening of contact 63 and the pilot motor 24 is stopped. I V

The speed of the running motor 11 may nowbeincreased through successive steps up to the maximum value by again closing the normally openedfhast control button.

Reversing switch 26 is again energized and connects the pilot motor 2 l'to. supply lines 15, 16 and 17 in the manner previously described. tinues the rotation of the speed controller 23 in a counterclockwise direct-ion and successively reduces the value of the resistances 20, 21 and 22 inthe secondary circuit of the motor 11, and finally short circuits the slip rings of the motor. To reduce the operating-speed of motor 11, the -Slowjog push button is closed. This establishes an energizing circuit for reversing switch 25 extending from the conductor 50 through the Safety switch andthe Slow-iog push button the conductor 51 the conductor- 71.

limit switch'72, conductor 73 and then through the, operating winding of reversing switch 25 to the supply line 15. lhe 're sultingclosure of reversing switch 25 connects the pilot motor as to the supply lines 15, 16 and 17 for operation in the'reverse Thereupon pilot motor 2 1 condirection thus operatingthe speed controller- 23 in a clockwise sition shown. 7

lit will be observed that when the running motor line switch 19 closes, an energizing circuit for the electroinagnet switch '37 is established upon the engagement of auxiliary contacts T4 with upper set of stationary contacts cooperating therewith. This circuit may be traced from the-supply line 15 through the middle blade of disconnecting switch 42, the conductor 50, contacts 7%, in the upper position and through the operating winding of electromagnetic switch 37: and theright hand blade of disconnecting switch 12, to the supply line 17. Hence, immediately upon the closure of running direction towards the pothe alternating current motor 33 of the motor generator set to thesupply lines 15, 16 and 1'? thus setting the direct current generator 34 into standby operation preparatory to energizing the operating winding of the electroniechanical brake 28 when the electromagnetic switch 38 is closed.

Vi henever the speed controller 23 is set near the maximum running speed position the contact engages with the se -merits 76 and the electron 'netic switch it) is energized through a circuit extending from supply line 16 through the middle blade o t switch conductor 50, conductor 77, segments '76 and contact 63, conductor "38 and the operating winding oi switch 40 to the supply line 12"," This causes the switch 4-0 to open the short circuit around the regulating resistance 39 in the shunt field circuit of: generator and thereby decreas the voltage generated by the lat This prevents full energization chanical brake 28 when the latter is applied withthe speed cont-roller 23 near the nu inuin speed position, and thereby effectively eliminates the shock and strain which would he occasioned by a full application of the electromechani al brake when the press is running at high eed. I

To stop the press when running at full speed, the normally closed Stop button is operated to the open position to interrupt the energizing circuit of line switch 19. Upon the resulting opening of line switch 19, the electroinec ianical brake 2'? deenergized and operates to the braking position accord ng to its bias simultaneously with the disconnection oft-he motor 11 from the supply lines 15, 16 and 17. [it the same time the electromagnetic switch 38 is ener--- gizecthrough a circuit extending from supply line 15 through the left hand blade of disconnecting switch 42, the contacts 01" overload relays 58, the auxiliaryccnas ant tact 7s of line switch 19 and the lower stationary contacts cooperating therewith, the operating winding of switch 38, conductor 79, segments and sliding contact 54 of the speed controller 23, conductor 81 and then through the middle blade of disconnecting switch to supply line 16. Switch 88 thereupon closes and connects the operating winding of the electromechanical brake 28 to the generator 34iand the hralre is applied with reduced power due to the de creased voltage of generator previously explained. It will be observed that closure of switch 38 also energizes the operating winding of the relay l1 through the auxiliary contact 83 with which switch 38 is provided and the relay 41iis set into operation to open its contact after a time interval determined by the retarding dash pot with which it is'provided.

Also upon the opening of line switch 19 of the electromerelease position according to its bias;

a circuit is established through the mint iary contact 69 and the lower stationary contact cooperating ther with together with the auxiliary contact 67 of switch 14 and the lower stationary contact cooperating therewith, conductor 82, limit switch 72, conductor 73, and the operating winding oi reversing switch which operat'vely ener gizes the letter from the supply lines 15 and 16] The resulting closure of reversing switch 25 connects the pilot motor 24: to the supply lines 15, 16 and 17 for operationot the speed controller 23 away from the maximum speed position toward the position in wh ch it is shown in the drawing.

Thus it will be seen that in'nnediately up on the opening of line switch 19 the electromechanical brake 25 is energized at the reduced voltageot generator 3-1 as previously pointed out and at the same time the relay a l is operatively energized and the PllOil motor 2% is also energized inthe manner just described.

After the predcterininec necessary for the pilot inotor 2-lto operate the speed controller 2:) to disengage the 7 time interval 7 contact from the segments 76, the electro-inagnetic switch is de-ei' gized and closes its contact to short circuit the field regulat ng resistance 39 of generator 34;. I

This ell ects a gradual increase in the voltage generated by the generator 3 during the period required the field to build up,

full strength and correspondingly increases the energization of the operatin ofttheelectrically operated hrelre 2S apply the latter with full power, combined braking etlect of the bralres27 and 28 thepress is brought to a standstill smoothly and gradually.

During the operatioi'ijust described the pilot motor 2% continues the rotetio'n olthe speed controller 23 in clockwise directi n towards the posit-ion shown in the drawing and after a predetermined time interjiuil el i'ects the d sengagement ol thesl-iding coir tact 5 1- from the segments 80. This opens the circuit through which the braking switch 38 was energized but the latter nevertheless is maintained energized through a shunt holding circuit including the auxiliary contact 84 of switch and the contact of the time relay 41. Hence, alter the predetern'iined time interval required for relay 421 to open its contact has elapsed, the brelting switch 38 is de-energized and disconnects the operating winding; 32 of the elec trically operated brake 28 from the generator Brake 28 thereupon returns to the V The opening of the contactof time element relay ll also interrupts the holding circuit of the electromagnetic switch 37 and the latter opens and disconnects the motor 33 of the -1notor generator set from the supply lines winding Due to the 15, 16 and 17. Thus it will 'be seen that the electrically operated brake 2-8 is released and the motor generator "set is shutdown a predetermined time interval after the opening of the energizing circuit for the running actor 11. Vv'hen the pilot motor 24 has rotated the speed controller 23,to the extreme position in which it is shown in the drawing, the engagement ofthe limit switch 72 opens the energizing circuit, of the reversing switch 25 and the latter operatcs'to disconnect the pilot motor 2% from the supply line. I

Thus, each of thecontrol elements of my improved control system are returned to their respective positions shown in the drawing preparatory to subsequent operation of the press responsive to operation of either of the normally opened control bi'ittons, Snow-jog and Fast respectively espreviously described.

In accordance with the provisions'of the patent statutes, I have described the principles of my invention together with'a prererred embodiment thereof but I would haye it understood'that the apparatus shown is only illustrative and that the invention may he carried out by other-means. a

What I claim as new and desire to secure by Letters'Pate-nt otthe United Statesis:

1. In a braking system" for an electric motor driven machine, the combination with switch mechanism for connecting the driving" motor of said machine to a sourceof supply and disconnecting the same therefrom, of an electrically operated friction brake for said machine, a separate source or" energizing current for said'brake, switch mechanism for connecting the said brake to said separate source to apply the brake upon the discon nection of the driving motor and automatic n'ieans for increasing the energization of said brake after the application thereof.

2. In. a braking system for an electric motor driven machine, the combination with switch mechanism for opening and closing an energizing circuit forthe driving motor, of an electrically operated brake for said ma chine, a variable voltage source of energizing current for said brake, switch mechanism for connectingthe said brake to said source to apply the brake upon the opening of the drivingmotor circuit, and automatic means for increasing the voltage 'of'said source after the application of said brake.

3. In a braking system for an electric motor driven machine, the combination with switch mechanism foropeningand closing an energiZing eircu'itffor:theidriving :motor, of an electrically operated friction brake for said machine,"a variable-voltage source of energizing current for said brake, electroin ietic switch mechanism controlled by said first switch mechanism for conn'e'cting thewsaid brahe*tosaid'sourcefto 'a t he I vice for transforming alternating'current to same upon "the openingfoftheidriving motor circuit, and automatiomeans for successively increasing the voltage of said sourceand disconnecting the said brake therefrom after the opening of the driving motor circuit. I

4-. in a braking system. for an electric motor driven machine, the combination with switch mechanism for opening and closing an, energizing circuit for the driving motor of said machine, of a plurality-of electrically operated friction brakes for said machine, one portion of which'is biased to the braking position and electrically operated there from and another portion of whi'ch is biased from the braking position'and electrically operated thereto, each portion of said brakes being arranged to be energized from a separate' supply source, switch mechanism con-' trolled l y said first mentioned switch mechanism for tie-energizing the'said one portion of said brakes andenergizingthe said other portionot' said brakes'upon the opening of the driving motor circuit, andautoratio means for de-energilzing the said sec end portion of saidbrakesatter the application'thcreof; V

5. In a braking system for an alternating current motor driven machine,'the combination with an electrically operated f-ri" on brake for said machine'nieans toreiiergizing said brake to apply thesame comprising device for transforming alternating current to direct current, switch mechanism for connectingsaid bralre'to the said device, and automatic means for controlling said first means to increase. the energiz'ation of said brake after the application thereof.

6. bra lring sy'stein for an alternating' current motor driven machine, thecomloination withineans for controlling'the"energization otthe driving motorofsaid machine, of an electrically actuated frictionbralre for said machine, means for energizing the said brake to apply thesame comprisinga da direct current, and s'witch'inechanism controlled by said first means for connecting the said device to a source ot alternati-ng current upontheenergizationof the driving-motor and to the said brake upon the de 'energi'za tion of the driving 'motor. 7

I 7. In a braking system for an alternating current motor driven machine, the comb mttion with switchmcch'anism foro'peiiing and closing an energizing circuit for the driving motor ofsaid machine, of'an electrically operated: friction I b'rakeflfor said; machine, means "fo ;ener i ing-the s i o plyi the same rem ri a dev formin alternat rent, switch "me p connecting the: said "deviceftoja source o' I alternatiiigci uponithe one zation or "the di g mot oi "d'na" n "aiidfto'the-sa' bia'e I r the said source and from said biai-le.

- the released position,

the said bi'alzc conipiisin of said generator after a time interval and generator.

8. In a braking system for an alternating current iiioto driven machine, the combination with switch mechanism for opening and closing an energizing circuit the driving motor of said machinepof a friction brake for said 'iiiacliiiie biased to means for applying V winding, a motor generator set for transforming alternating current todirect current, and switch mechanism for connecting the motor of said set to a source of alternating current upon the energization of the driving motor of said 'lllafilllnfi and for connecting the said winding to the generator of said set upon the derenergization of the driving motor of said machine, and automatic means set int operation upon the de-energizatioii of the driving motor for increasing the voltage for thereafter disconnecting the motor of said set from the said source and the generator of said set from said winding.

O. In a braking system for a i l illllispeed alternating current motor driven machine, the combination with'means for controlling the energization and speed of the, driving motor of said machine, of an electrically actuated friction brake for said machine, means for energizino' said brake to apply the same compris a motor generator set for transforming alternating current to direct current, switch mechanism for con- I iiectiiig the motor ofsaid set to a source of alternating current upon the energization of the driving motor of said machine and "for connecting thegenerator of said. set to the said bra-he upon the de-cnergization of,

the driving motor of said machine, and i'iieans dependent upon operation of the said speed controlling means of the driving motor for controlling the, voltage of said 10. In a braking system for a motor driven machine arranged to be operated at a definite low speed and at a higher speed, the combination of two electrically controlled frictioii brakes for said machine, the

n a a I v 1 first or said brakes being biased to toe brakmg position and electrically operated therefrom and the second of said brakes bein D biased to the released position and electrically operated to theapplied position, and switch mechanism aiidconiiections controlled thereby whereby the first of said brakes is released when the machine is operated at either of said speeds and is applied to retard the machine after operation at either of said speeds and the second of said brakes is applied, to retard the machine after operational; the high speed.

11. In a braking system for an electric motor driven machine, the combination with manually controlled means for operating the said machine at low speed and at high speed, of a plurality of electrically operated friction brakes for said machine,

one portion of which is biased to the brak ing position and electrically operated there" 12. In a braking system for an electric motor driven machine, the combination with a driving motor for operating the said machine at slow speed, a second driving motor for operating the said machine at a plurality of running speeds, switch mechanism selectively operable to connect each of said motors to asoiirce of supply and to control the speed of said second motor, of

a plurality of electrically operated friction brakes for said machine, one portion of which is biased to the braking position and electrically operated therefrom and another portion of which is biased from the brain ing position and electrically operated'there to, switch me 'haiiism controlled by said first mentioned s. i ch mechanism for energizing and deenergizing the said one portion of said brakes simultaneously with'the energization and deeiiergization of said motors, and electromagneticswitch niechanism controlled by said first mentioned switch mechanism for energizing the said other portion. of vsaid brake to apply the same upon the; second motor. r I

v13. In a braking system for a variable speed alternating current motor "drivei machine, the combination with means forcoiitrolling the energizatioii and speed oftlie driving motor of said machine, of a pliirality of electrically operated friction brakes for said machine, one portion of which is biased to the braking position and elecf trically operated therefrom and another portion of which is biased from the. braking position and electrically operated thereto, means for energizing the said second portion of said brakes to apply the same comprising a device for transforming alternating current to direct current, switch mechanism for connecting 'thesaid device deeiiergization of said l and the said first portion of said brakes to a source of alternating current upon the energization of the driving motor of said machine and for connecting the said device to the said second portion of said brake and disconnecting the said first portion of said brakes to apply the same upon the def energization of the driving motor of said machine, and automatic means, for increasing the energization of said second portion of said brake aiter'the application thereof.

1%. In a braking system for a variable speed alternating current motor driven machine, the combination with means for controlling t-he energization and speed of the driving motor of said machine, oi a plurality of electrically operated friction brakes for said machine, one portion of Which is biased to the braking position, and electrically operated therefrom, anctanother portion of which is biased from the braking position and electrically operated thereto, means for ener izing the said second portion of said brakes to apply the same comprising a motor generator set for trans rent upon the energization of the driving motor of said machine and for disconnecting the said first portion of said brakes from said source and connecting the generator of said set to the said second portion of said brakes upon operation of the de energizatlon of the driving motor of said machine, means dependent upon the said speed controlling means of the driving motor for controlling the voltage of saidv generator, and automatic meansset into operation upon the deenergization of the driving motor for successively increasing the voltage of said generator and disconnecting the motor of said set -from the said source and the generator of said set from said second portion of said brakes.

In witness whereof, I have hereunto set my hand this 28th day of May, 1924:. i v

ROY N, THOMAS.

Certificate of Correction.

It is hereby certified that in Letters Patent No. 1,585,439, granted May 18, 1926, upon the application of Roy N. Thomas, of East Orange, New Jersey, for an imrovement in Electric Braking Systems, an error appears in the printed specification requiring correction as follows: PageT, line 35, claim 1. 1, strike out the Words operation of and insert the same to follow after the Word upon, line 37, in same claim; and that the said Letters Patent should be reacl With this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed. this 13th day of July, A. D. 1926.

[SEAL] M. 'J. MOORE,

Acting Commissioner of Patents. 

